Julian Castro (c.), mayor of San Antonio, accompanied by his brother, Rep. Joaquin Castro (D) of Texas (2nd from r.), prepares to testify before a House Judiciary Committee hearing on immigration on Feb. 5.

Should immigration reform legislation offer people living in the United States illegally a (long) pathway to citizenship? Or would some intermediate step such as legal residency suffice?

That’s a debate that arose this week at a House Judiciary Committee hearing on the prospects for fixing America’s rickety immigration system. It’s not a simple argument, given that it involves national and immigrant identity, the reasons some risk their lives to sneak across the US border, simple fairness, and practical considerations about the design of any new immigration system.

It also, perhaps, presages the difficult policy arguments to come as the effort to craft a 2013 reform bill picks up momentum in Congress.

Right now, an estimated 11 million to 12 million illegal immigrants are already in the country. President Obama supports providing them a way to eventually qualify for US citizenship. Some Republicans are beginning to come out in support of the same thing, given their party’s lack of success in attracting Hispanic voters.

The so-called Gang of Eight bipartisan Senate immigration proposals, for instance, would require individuals here illegally to register with the government, pay a fine and back taxes, and undergo a background check. In return, they’d get probationary legal status – and the opportunity to stand in the back of the line to get eventual US citizenship. Everyone who’s already in that line, legally, would get their opportunity first.

“Our purpose is to ensure that no one who has violated America’s immigration laws will receive preferential treatment as they relate to those individuals who have complied with the law,” states the proposal, backed by Republican Sens. Marco Rubio of Florida and John McCain of Arizona, among others.

This would be contingent on tighter border security – a linkage Mr. Obama and many other Democrats oppose.

Many in the GOP oppose this approach, however. They label it “amnesty” and a draw for future illegal immigrants, who will come to the US believing that eventually they will receive similar treatment.

Rep. Raul Labrador (R) of Idaho, for instance, argued at the House hearing that, in his years serving as an immigration lawyer, he has talked to thousands of people living here illegally, and that what they want is not citizenship per se, but to come out of the shadows, live and work legally, and be treated with dignity.

“So if we can find a solution that is short of a pathway to citizenship ... but better than just kicking 12 million people out, why is that not a good solution?” said Representative Labrador.

The answer, said San Antonio Mayor Julian Castro, a hearing witness, is that an intermediate solution would create a class of permanent second-class residents.

He and other Democrats argued that the experience of many nations in Europe, who have admitted immigrants from Turkey and other Eastern nations under such an arrangement, shows that it breeds separatism and resentment. The US has always allowed legal residents a path to citizenship, Democrats pointed out – with the exception of slavery and the Chinese Exclusion Act of 1882.

“Throughout the history of this nation, the biggest challenges we’ve faced have been when we created second-class citizens, much less second-class noncitizens. And so I believe that a path to citizenship is the best option,” said Mr. Castro.

The path to citizenship outlined in the Senate’s immigration plan is not a short one. Given the current backlog of those who have legally applied for such status, it would likely be at least a decade before current illegal immigrants would be able to satisfy all criteria and reach the head of the line.

And as Labrador pointed out, not all want to go through the process. A new Pew Research Center poll notes that nearly two-thirds of the 5.4 million legal immigrants from Mexico who are eligible to apply for citizenship have not done so. Mexicans are by far the largest group of both legal and illegal US immigrants.

Pew’s findings suggest that not all Mexicans now living in the US shadows would jump at the chance to stand in the citizenship line.

“Many could choose an intermediate status – legal permanent resident – that would remove the threat of deportation, enable them to work legally and require them to pay taxes, but not afford them the full rights of US citizenship, including the right to vote,” write Pew Research Hispanic Center analysts.

People of other nationalities might not feel the same way, however. As Pew notes, 68 percent of eligible immigrants from countries other than Mexico have opted for the citizenship route. And among Mexicans who have not applied, only about one quarter say it is because they do not wish to. Twenty-six percent say it is due to language and other personal barriers. Eighteen percent say it costs too much.

It’s not just a matter of nomenclature, after all. Citizenship conveys the right to vote. Given the current tilt among Hispanics toward Democrats, that could raise objections from Republicans in the weeks and months ahead.

Citizenship also provides access to a much larger array of government benefits.

Illegal immigrants are barred from such programs, and indeed all federal public benefits, with the exception of emergency aid. But there’s a “widely-held perception” that many get access to these programs anyway, says the CRS study.

Despite the emotions that can surround the citizenship debate, one thing all sides might support is legislation that would officially place children brought to the US by illegal immigrant parents on a citizenship track, suggested Vivek Wadhwa, a visiting scholar at the University of California, Berkeley, and a witness at Tuesday’s House hearing.

“I believe that if we provided green cards to all the undocumented workers immediately, if we give their children citizenship, and if we fix the skilled immigrant problem, there will be consensus nationwide,” said Mr. Wadhwa. “And we don’t have to get into these toxic battles about citizenship or not citizenship.”

According to recent polls, the US public as a whole approves of offering citizenship to undocumented residents. A recent ABC News/Washington Post poll found 55 percent of respondents supported such a path to citizenship, and 41 percent were opposed. The partisan breakdown hinted at the political difficulties ahead: 68 percent of Democrats and 52 percent of independents approved of the idea. Republicans opposed it, 42 percent to 54 percent.